The present disclosure relates to a wireless LAN system including a wireless terminal and a base station wirelessly communicating with each other, and a wireless communication device communicating with a base station.
A wireless LAN system standardized by IEEE802.11 performs roaming to change the base station currently connected to a wireless communication device (wireless terminal) to an alternative base station. When the level of radio waves received from the connected base station lessens and the quality of communication between the wireless terminal and base station cannot be ensured, for example, the wireless communication device roams to another base station that can provide better quality communication with the wireless communication device.
In the process of roaming, the wireless terminal searches for base stations which can be candidates for the alternative base station and previously acquires information on the candidates before roaming from the connected base station to another base station. This can shorten the time taken to roam from the connected base station to the alternative base station.
The methods by which the wireless terminal searches for base stations include active scanning and passive scanning. With an active scan, the wireless terminal transmits a probe request message. With a passive scan, the wireless terminal waits for beacons transmitted from base stations.
In the active scan, after receiving a probe response message from a base station within a time called MinChannelTime, the wireless terminal must continue searching during the time called MaxChannelTime. If the wireless terminal cannot find any other base station, the time corresponding to the difference between MaxChannelTime and MinChannelTime is exhausted.
In the passive scan, the wireless terminal must continue searching during MaxChannelTime. Accordingly, if the wireless terminal cannot find any other base station, the time corresponding to MaxChannelTime is exhausted.